1. Field of the Invention
This present invention relates to a charge circuit, and more specifically to a multi-cell battery pack charge balance circuit.
2. The Related Art
At present, a portable electronic product has a battery pack which includes lots of battery cells connected each in series, and each battery cell has a different inner resistors. During charging process, when one battery cell has finished charging while the other battery cells have yet not finished charging, any battery cell will open the over voltage protection function once fully charged by the charge circuit to prevent further charging, and consequently, the charging process of the whole battery pack will be terminated unduly because of actuation of the over-voltage protection circuit of the fully charged battery cell, thereby causing other battery cells of the battery pack can not be charged to a saturation level synchronously.
For overcoming the drawback described above, a conventional multi-cell battery pack charge balance circuit is developed and disclosed in FIG. 1, which includes a first and second control circuit parallel connected with a battery pack 100. The battery pack 100 includes a first battery cell 101 and a second battery cell 102. The first control circuit includes a first switch 201 and a first resistor 301 connected with the first switch 201 in series. In a similar manner, the second control circuit includes a second switch 202 and a second resistor 302 connected with the second switch 202 in series. In charging, if the first battery cell 101 achieves a charge balance firstly, the first switch 201 will be switched on such that part current will flow through the second battery cell 102 via the first resistor 301 and the first switch 201 to prevent the first battery cell 101 starting the over voltage protection function which is capable of terminating the charging process and accordingly, the second battery cell 102 is charged in succession until the second battery cell 102 achieve a saturation charging state.
Because the current in the conventional charge circuit is very large, when the first switch element 201 is on, a large current will passes through the first battery cell 101, resulting in a weak charge balance.